CDMA, Globalstar versus Iridium, Inmarsat, etc. Message Board

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Technology Stocks : CDMA, Globalstar versus Iridium, Inmarsat, etc.

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To: doormouse who wrote (158)	6/18/1997 5:42:00 PM
From: Maurice Winn	of 381

Kibo, satellites crashing into each other is not generally considered to be good. Shooting competitors' satellites is also frowned on. The photovoltaic panels get a bit bent if they bump and the satellites get the wobbles which mucks up signal directions. If they are going in opposite directions the effect is more like a subatomic particle supercollider and the two disappear in a supernova of radio transmission. They have spares in orbit for just such events. Mostly the satellites are going in much the same direction though, because they want to save fuel which they do by launching in the direction of the earth's rotation - it gives them 1000 km per hour headstart. By travelling the same direction as the earth, they also get to spend a little longer between horizons, meaning fewer handoffs to other satellites are needed. Globalstar and Iridium will circle earth on inclined planes, and have about 10 minutes in view, whereas the geostationary satellites stay over the equator, but far away, so they always stay in the same position relative to an observer and only three of them enable all points on earth to see one of them. [Just to explain for viewers who are unfamiliar with these things]. Leo is always better than Geo because the signal is half a second quicker. That doesn't seem long, but anyone who has tried talking via Geo knows that the delay and verbal miscues as both wait for the other to start speaking, then both start simultaneously, then both stop makes for very disjointed conversations. People are better to revert to old radio lingo: "Hi Fred! Over." "G'day mate! Over" "Is it raining there? Over" "Nah! Fairly sunny for the middle of winter. Over". Or get a CDMA Leo phone. The doppler shift for satellites moving relative to people running around on the ground is not great. While the satellite does glow faintly red due to the red-shift caused by relativity effects on the wavelength of the radio photons, the CDMA system handles this easily. Hence CDMA Leo is the way to go. Maurice

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